Verhalten von Sulfatgestein im Tunnelbau – Erfahrungen aus Feldbeobachtungen und In‐situ‐Quelldrücke

Tunnels and underground works in sulphate bearing rocks are very challenging. For more than a century experience has accumulated in Switzerland and southern Germany with difficult conditions during construction and operation, which show the difficult conditions with extreme, long lasting heave of the invert and extreme swelling pressures. The analyses of published experience over more than a century and recent personal experience led to the compilation of many pieces of a puzzle and to a better understanding of complex processes. The swelling processes in sulphate bearing rocks are triggered by the formation of flow path for water, the dissolution, concentration and precipitation of minerals. In particular Anhydrite is dissolved and the solution becomes saturated, until precipitation and crystallization of Gypsum starts. The applied construction methods play an important influence on the rock mechanics and geochemical processes and finally the magnitude of in‐situ swelling pressures. The in‐situ swelling pressure are still large, but substantially less than the swelling pressures from laboratory tests. Estimated swelling pressures will be indicated.